Fujimura Ken, Kano Fumi, Murata Masayuki
Department of Life Sciences, Graduate School of Liberal Arts and Sciences, University of Tokyo, Tokyo, 3-8-1 Komaba, Meguro-ku, 153-8902, Japan.
RNA. 2008 Mar;14(3):425-31. doi: 10.1261/rna.780708. Epub 2008 Jan 3.
Recent advances in microscopic techniques have shed light on the roles of specific subcellular structures in the regulation of gene expression. One such structure is the stress granule (SG), which is engaged in stress-triggered translational arrest by sequestering pre-initiation complexes of translation. Recent studies revealed the spatial, compositional, and functional linkage of the SG to the processing body (P-body), another cytoplasmic structure that has been implicated in mRNA degradation and siRNA- or miRNA-mediated gene silencing. In this study, we report that PCBP2, a facilitator of IRES (Internal Ribosomal Entry Site)-mediated translation, is a novel constituent of the SG and P-body. Immunofluorescence studies revealed that while PCBP2 is diffusely distributed throughout the nucleoplasm and the cytoplasm, the protein is enriched in a subset of P-bodies under normal conditions. Upon exposure to heat and arsenic stress, PCBP2 became predominantly accumulated at the SG, but was still present in Dcp1a-positive P-bodies. Live-cell imaging revealed the dynamic association of PCBP2-enriched P-bodies and the SG, and FRAP experiments demonstrated that PCBP2 actively moves in and out of the SG and P-body. Taken together, these results suggest that PCBP2 shuttles between the cytoplasm and the two structures under stress. We propose that PCBP2 may be involved in stress-induced remodeling of mRNP complexes and that it may also play a role in the rapid transition of certain silenced mRNAs into a translationally active state. Additionally, given the property of PCBP2 as a nuclear-cytoplasmic shuttling protein, PCBP2 may play a role in directly targeting nascent mRNPs to specific P-bodies for storage.
显微镜技术的最新进展揭示了特定亚细胞结构在基因表达调控中的作用。其中一种结构是应激颗粒（SG），它通过隔离翻译起始前复合物参与应激触发的翻译停滞。最近的研究揭示了SG与加工小体（P小体）在空间、组成和功能上的联系，P小体是另一种与mRNA降解以及siRNA或miRNA介导的基因沉默有关的细胞质结构。在本研究中，我们报道了PCBP2，一种内部核糖体进入位点（IRES）介导翻译的促进因子，是SG和P小体的一种新成分。免疫荧光研究表明，虽然PCBP2在整个核质和细胞质中呈弥散分布，但在正常条件下该蛋白在一部分P小体中富集。在受热和砷胁迫时，PCBP2主要聚集在SG处，但仍存在于Dcp1a阳性的P小体中。活细胞成像揭示了富含PCBP2的P小体与SG之间的动态关联，荧光漂白恢复（FRAP）实验表明PCBP2能活跃地进出SG和P小体。综上所述，这些结果表明PCBP2在应激条件下在细胞质与这两种结构之间穿梭。我们提出，PCBP2可能参与应激诱导的mRNA核糖核蛋白复合物重塑，并且它可能在某些沉默mRNA快速转变为翻译活性状态中也发挥作用。此外，鉴于PCBP2作为一种核质穿梭蛋白的特性，PCBP2可能在将新生的mRNA核糖核蛋白直接靶向特定的P小体进行储存方面发挥作用。
